1. Field of the Invention
The present invention relates to a presser regulating thumb screw device of a sewing machine.
2. Prior Art
As a presser regulating thumb screw device of a sewing machine, there is known for example, a presser regulating thumb screw device for an overlock sewing machine shown in FIG. 9. In the figure, denoted by 50 is a bed of a sewing machine, 51 is an arm of a sewing machine, 52 is a presser foot, and 53 is a needle. The presser foot 52 is fixed to a presser bar 54, and a presser regulating thumb screw 55 is disposed on the upper end of the presser bar 54. The presser regulating thumb screw 55 is fixed to the bed 51 of the sewing machine by screwing a male portion 55c thereof to a female portion of the arm 51 of the sewing machine, wherein a head 55a formed at the upper end of screw 55 protrudes outward from the upper surface of the arm 51. The head 55a is a slotted head, namely, slotted grooves 55b are formed therein so as to extend radially as shown in FIG. 8.
In this sewing machine, a pressure by the presser foot 52, i.e., a pressure for pressing a material to be sewn (workpiece), not shown, onto the bed 50 of the sewing machine is adjusted as follows. Namely, the presser regulating thumb screw 55 is turned clockwise or counterclockwise manually or by the use of a coin or a special instrument inserted into the slotted grooves 55b. Thus, the presser regulating thumb screw 55 screwed into the female portion of the arm 51 of the sewing machine is screwed in or screwed out, thereby extending or contracting a presser bar spring (not shown) interposed in a pressed state between the presser regulating screw 55 and the presser bar 54. In this manner, the force to press the workpiece downward by the presser bar 54 which receives repulsive force of the presser bar spring and by the presser foot 52 is adjusted to increase or to decrease, thereby adjusting the pressing force.
However, the prior art presser regulating thumb screw device of a sewing machine has following technical problems.
That is, the presser regulating thumb screw 55 has to maintain a smooth operation of the presser bar 54 by forming a through hole comprising a little diameter hole and a large diameter hole extending in the central axial direction thereof in an ascending order, and receiving the upper end of the presser bar 54 into this through hole so as to be slidable therein, and supporting the presser bar 54 by the small diameter hole alone. Because of this, it is hardly avoidable that the large diameter hole is open at the head 55a at the upper end of the presser regulating thumb screw 55. This is caused by the fact that it is not easy to define a large diameter hole in the intermediate portion of the presser regulating thumb screw 55 in the axial direction thereof. As a result, the slotted grooves 55b at the upper end are formed of a pair of grooves having a large distance therebetween.
Therefore, a usable instrument that can fit the slotted grooves 55b is limited, which makes it impossible to use a general instrument having an operation part of a narrow width such as a driver, etc. In addition, since the top 55a of the presser regulating thumb screw 55 must protrude outward from the upper surface of the arm 51 of the sewing machine, the workpiece and a sewing thread are liable to be caught by the protrusion, which interrupts sewing operability and restricts designing of the upper part of the sewing machine.
Means to Solve the Problems!
The present invention has been made to solve such technical problems of the prior art presser regulating thumb screw device and comprises as follows.
A presser regulating thumb screw device of a sewing machine according to a first aspect of the invention comprises a presser regulating thumb screw device of a sewing machine screwed into an arm 2 of a sewing machine and including a presser regulating thumb screw 18, the presser regulating thumb screw 18 being turned clockwise or counterclockwise for regulating to increase or decrease a pressing force by a presser foot 6, wherein the presser regulating thumb screw 18 comprises a screw body 8 and a fitting member 9 fitted in the screw body 8, the screw body 8 is bored in a central axis thereof to form a small diameter fitting hole 8a, a large diameter receiving hole 8b having a diameter larger than that of the fitting hole 8a and a spot facing part 8c extending from the large diameter receiving hole 8b having a diameter larger than that of the large diameter receiving hole 8b, the small diameter fitting hole 8a, the large diameter receiving hole 8b and the spot facing part 8c are arranged in an ascending order, and wherein the fitting member 9 is fixed to the spot facing part 8c so as not to turn relative to the spot facing part 8c, and the fitting member 9 has a fitting part 9b, the fitting part 9b having a different shape other than a circular shape in cross section.
A presser regulating thumb screw device of a sewing machine according to a second aspect of the invention comprises a presser regulating thumb screw device of a sewing machine according to claim 1, wherein the fitting member 9 is discoidal and has a plurality of protrusions 9a at a given interval on an outer periphery thereof in a circumferential direction, and the spot facing part 8c is formed of a circular hole, and wherein the fitting member 9 is pressed and fixed to the spot facing part 8c in a state where each protrusion 9a is deformed.
A presser regulating thumb screw device of a sewing machine according to a third aspect of the invention comprises a presser regulating thumb screw device of a sewing machine according to claim 1 or 2, wherein the arm 2 of the sewing machine comprises an arm cover 2b covering an upper outer side of the arm body 2a of the sewing machine, the presser regulating thumb screw 18 is screwed into the arm body 2a of the sewing machine, and wherein the arm cover 2c has a through hole 2c through which an instrument is inserted at a part thereof corresponding to the presser regulating thumb screw 18.
According to the first aspect of the invention, the force to press the workpiece on the bed of the sewing machine by the presser foot 6 is regulated as follows. Namely, the tip end of an instrument (e.g. a driver) is fitted in the fitting part 9b of the fitting member 9. When the instrument is turned clockwise or counterclockwise in this state, the screw body 8 is turned via the fitting member 9 pressed in and fixed to the spot facing part 8c, and the presser regulating thumb screw 18 screwed by the male screw 8g is screwed into or out of the arm 2 of the sewing machine. The downward pressure of the presser foot 6, i.e., the pressing force against the bed 1 of the sewing machine by the presser foot 6 is regulated to be increased or decreased owing to the movement of the presser regulating thumb screw 18 when it is screwed into or out of the arm 2 of the sewing machine. Since the spot facing part 8c is formed in a state that the receiving hole 8b is open, the screw body 8 can be integrally formed of synthetic resin and can be comprised of the fitting hole 8a and the receiving hole 8b which is provided at the intermediate portion thereof and is larger than the fitting hole 8a in a diameter thereof.
According to the second aspect of the invention, since the fitting member 9 is pressed in and fixed to the spot facing part 8c of the screw body 8 so as not to turn relative to the spot facing part 8c and not to be pulled out, the fitting member 9 and the spot facing part 8c of the screw body 8 can be easily manufactured, and pressing operation of the fitting member 9 can be easily done, and the fitting member 9 is difficult to be deformed or pulled out when pressing force is repeatedly regulated.
According to the third aspect of the invention, the tip end of the instrument (driver) is inserted from the through hole 2c of the arm cover 2b, and the tip end of the instrument is fitted in the fitting portion 9b of the fitting member 9. In this state, when the instrument is turned clockwise or counterclockwise, presser of presser foot 6 against the bed 1 of the sewing machine is regulated to be increased or decreased.